Portable positioning devices and methods for obtaining a geospatial position

ABSTRACT

Embodiments provide for methods and portable positioning devices adapted to determine a geospatial position of a point of interest. In one embodiment, the portable positioning device comprises an antenna, a levelling detector, an imaging device, a display unit and a processing unit. The antenna may be adapted to receive satellite information signals. The levelling detector is arranged relative to the antenna for detecting whether the antenna is positioned horizontally. The imaging device has an optical axis and a sighting axis. In one embodiment, the sighting axis intersects an antenna axis. In another embodiment, the sighting axis is aligned with the antenna axis. The display unit may be provided for assisting in identifying the point of interest within a field of view of the imaging device and for assisting in identifying whether the antenna is horizontally levelled and whether a phase center and the point of interest are vertically aligned.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to EPC Application No.18290087.8, filed Jul. 20, 2018, the contents of which are incorporatedherein by reference in their entirety for all purposes.

TECHNICAL FIELD

The present disclosure relates generally to the field of positioningand, more particularly, to methods and portable positioning devices forobtaining a geospatial position of a point of interest. Positioningdevices disclosed herein may provide a two-dimensional, or athree-dimensional, geospatial position of the point of interest.

BACKGROUND

Positioning relates to the art of determining the position of a person,object or system on, or near, the surface of the Earth, i.e. the art ofdetermining the coordinates of a location (latitude, longitude andaltitude). Positioning may be of interest in, for example, the technicalfield of surveying whose purpose is to e.g. establish land maps based onthe determination of terrestrial or three-dimensional position of pointsusing the relative distances and angles between these points. In such anapplication, the resulting land map will be dependent on the absoluteposition of the surveying system, a component of the surveying system ora surveyed object, as may be determined by a positioning device usingsignals received from a global navigation satellite system (GNSS).

The position of a terrain point may for example be obtained by means ofa survey pole equipped with a pointing tip to place the survey pole atthe terrain point of interest and with a GNSS antenna having a so-called“phase center” at which satellite information signals are received. Thesurvey pole may also be equipped with a tilt sensor to level the surveypole so that it is ensured that the phase center of the antenna isvertical over the terrain point. Levelling the pole may however taketime and/or be imprecise. Further, as the satellite information signalsare received at the phase center of the GNSS antenna, compensation forthe length of the pole is necessary in order to compute thethree-dimensional position of the terrain point.

Such survey poles are commonly used in surveying applications. However,for such applications and also others, there is still a need ofproviding new and improved positioning devices. In particular, there isa need of providing more compact positioning devices.

SUMMARY

It is therefore an object of the present invention to overcome at leastsome of the above mentioned problems, and to provide an improved methodand an improved positioning device for obtaining a geospatial positionof a point of interest.

This and other objects are achieved by means of a positioning device anda method as defined in the appended independent claims. Otherembodiments are defined by the dependent claims.

According to embodiments of the present disclosure, there is provided aportable positioning device comprising an antenna, a levelling detector,an imaging device, a display unit and a processing unit.

The antenna may have a phase center and may be adapted to receivesatellite information signals from a GNSS at its phase center. In otherwords, the portable positioning device is equipped with a GNSS receivingunit including an antenna that is adapted to receive GNSS data. Theantenna may be referred to as the GNSS antenna in the following. Theantenna also includes an antenna axis which is a vertical axis passingthrough the phase center of the antenna.

The levelling detector may be arranged relative to the antenna fordetecting whether the antenna is positioned horizontally. In otherwords, the levelling detector may be arranged relative to the antennafor detecting whether the antenna is horizontally levelled, i.e. whetherthe antenna is positioned parallel to the horizon (or perpendicular tothe vertical as defined by the gravity field). The levelling detectormay be arranged to detect a deviation from a horizontal position. Thelevelling detector may be an inclinometer (a tilt sensor) or an inertialmeasurement unit, for example.

According to a first aspect of the present disclosure, the imagingdevice may have a sighting axis and the phase center of the antenna maybe arranged along, or at least close to, the sighting axis of theimaging device. The display unit may be provided for assisting, forexample an operator of the positioning device, in identifying the pointof interest within a field of view of the imaging device and forassisting in identifying whether the antenna is horizontally levelledbased on an input from the levelling detector and whether the phasecenter and the point of interest are vertically aligned, or at leastclose to vertically aligned.

Further, the processing unit may be configured to trigger computation ofthe geospatial position of the point of interest based on the satelliteinformation signals (or GNSS data) received at the antenna for aposition of the positioning device for which an indication that theantenna is horizontally levelled and the phase center of the antenna isvertically, or close to vertically, aligned with the point of interestis received.

According to a second aspect of the present disclosure, the sightingaxis of the imaging device may intersect the antenna axis at a certainangle. The sighting axis is an axis passing through a fiducial markerprovided in the field of view of the imaging device for assisting insighting the point of interest. The position of the fiducial markerwithin the field of view is dependent on a distance at which thepositioning device is held above the point of interest. The display unitmay be provided for assisting, for example an operator of thepositioning device, in identifying the point of interest within a fieldof view of the imaging device and for assisting in identifying whetherthe antenna is horizontally levelled based on an input from thelevelling detector and whether the point of interest is along thesighting axis. The processing unit may then be configured to triggercomputation of the geospatial position of the point of interest based onthe satellite information signals (or GNSS data) received at the antennafor a position of the positioning device for which an indication thatthe antenna is horizontally levelled and that the point of interest isalong the sighting axis is received.

According to a third aspect of the present disclosure, the imagingdevice is inclined with respect to the antenna such that the opticalaxis intersects the antenna axis. In the present aspect, a projectioncenter of the imaging device, through which the optical axis passes, islocated on the antenna axis. The display unit is then provided to assistin sighting the point of interest using a sighting axis and forassisting in identifying whether the antenna is horizontally levelledbased on an input from the levelling detector. The sighting axis passesthrough the projection center and a fiducial marker provided in thefield of view of the imaging device for assisting in sighting the pointof interest. The fiducial marker is located on the antenna axis. Theprocessing unit is then configured to trigger computation of thegeospatial position of the point of interest based on the informationsatellite signals received at the antenna for a position of thepositioning device for which an indication that the antenna ishorizontally levelled and the point of interest is along the sightingaxis is received.

In some embodiments, the processing unit of the positioning device maybe configured to itself compute the geospatial position of the point ofinterest based on the collected satellite information signals. In theseembodiments, the processing unit then computes the geospatial positionof the target (or point of interest) for the position of the positioningdevice for which the indication has been received. An operator of thepositioning device may thus position the positioning device above thepoint of interest such that the antenna is horizontally levelled and thephase center is vertically, or close to vertically, aligned with thepoint of interest, and the processing unit may, based on an indicationthat these conditions are fulfilled (i.e. the horizontal and verticallevelling of the positioning device), computes the geospatial positionof the point of interest for this position of the device. However, insome other embodiments, the positioning device (or its processing unit)may be in communication with a server, or an external device, havinganother processing unit at which computation of the geospatial positonmay be performed based on information related to the collected satelliteinformation signals. The processing unit at which the geospatialposition is computed may for example reside inside a remote serverlocated within an internet cloud infrastructure. The positioning device(or its processing unit) may then be adapted to provide the server, orthe external device, either with the geospatial position computed at thepositioning device or with the GNSS data collected and/or detected bythe GNSS antenna, the levelling detector, the display unit and/or theimaging device. In the latter case, the positioning device may thenreceive the geospatial position computed by the server or the externaldevice such that it may, for example, be displayed to an operator of thepositioning device.

It will be appreciated that the processing unit may also be referred toas a collector unit as the primary function of the processing unit is tocollect the satellite information signals received at the antenna forobtaining the geospatial position of the point of interest. Theprocessing unit or collector unit may then be in communication with theGNSS receiving unit including the GNSS antenna to receive the data. Ifthe computation of the geospatial position of the point of interest isperformed at a remote processing unit, the processing unit or collectorunit is then in communication with this remote processing unit totransmit information based on the collected satellite informationsignals. For example, this information may be raw GNSS measurements or adigitization of the collected satellite information signals.

Further, the processing unit may also be referred to as a control unitas the same unit may have the function of computing the geospatialposition of the point of interest and the function of controlling thedisplay unit and/or the imaging device, for example.

In some other embodiments, these functions of collecting, controllingand processing may be located in separate units in communication witheach other.

According to an embodiment, there is provided a method implemented in apositioning device comprising an antenna, a levelling detector, adisplay unit and an imaging device. The antenna may be adapted toreceive satellite information signals from a global navigation satellitesystem and the antenna may have a phase center. The levelling detectormay be arranged relative to the antenna for detecting whether theantenna is positioned horizontally. The imaging device has a sightingaxis and the phase center of the antenna is arranged along, or at leastclose to, the sighting axis. The method implemented in the positioningdevice may comprise determining whether the antenna is horizontallylevelled based on an input from the levelling detector, displaying thedetermination on the display unit for assisting (for example a user) inidentifying whether the antenna is horizontally levelled and displaying,on the display unit, images captured by the imaging device for assisting(the user) in identifying a point of interest within a field of view ofthe imaging device and in identifying whether the phase center of theantenna and the point of interest are vertically, or at least close tovertically, aligned. Based on an indication that the antenna ishorizontally levelled and that the phase center and the point ofinterest are vertically aligned, or at least close to verticallyaligned, the method further includes triggering computation of thegeospatial position of the point of interest based on the informationsatellite signals received at the antenna for the position of thepositioning device for which the indication is received.

According to another embodiment, there is provided a method which isequivalent to the method described above except that the sighting axis,which passes through a fiducial marker provided in the field of view ofthe imaging device for assisting in sighting the point of interest,intersects the antenna axis, which is the vertical axis passing throughthe phase center of the antenna. In the present embodiment, the positionof the fiducial marker within the field of view is dependent on adistance at which the positioning device is held above the point ofinterest. Based on an indication that the antenna is horizontallylevelled and the point of interest is along the sighting axis, themethod includes triggering computation of the geospatial position of thepoint of interest based on the information satellite signals received atthe antenna for the position of the positioning device for which theindication is received. In the present embodiment, the imaging device isinclined with respect to the antenna such that the optical axisintersects the antenna axis.

According to yet another embodiment, there is provided a method which isequivalent to the method described in the preceding embodiment exceptthat a projection center of the imaging device, through which theoptical axis passes, is located on the antenna axis. In the presentembodiment, the sighting axis and the antenna axis coincides. Thesighting axis passes through the projection center and the fiducialmarker provided in the field of view of the imaging device for assistingin sighting the point of interest. The fiducial marker is located on theantenna axis. Based on an indication that the antenna is horizontallylevelled and the point of interest is along the sighting axis, themethod includes triggering computation of the geospatial position of thepoint of interest based on the information satellite signals received atthe antenna for the position of the positioning device for which theindication is received.

As mentioned above, the methods may either include computing thegeospatial position of the point of interest locally at the positioningdevice or transmitting information based on the satellite informationsignals (GNSS data) collected/detected by the GNSS antenna to aremote/external processing unit for obtaining the geospatial position.

It will be appreciated that, in the above embodiments, the indicationthat the antenna is horizontally levelled and that the phase center andthe point of interest are vertically aligned, or at least close tovertically aligned (or in other words that the point of interest isalong the sighting axis), i.e. the trigger for computing the geospatialposition of the point of interest may be a user input. By means of theinformation provided at the display unit with respect to the horizontallevelling of the antenna and the positioning of the phase centervertically above the point of interest, the operator of the positioningdevice can decide whether the horizontal levelling and the verticalpositioning is satisfying and then trigger the computation of thegeospatial position of the point of interest based on the collected GNSSdata. Alternatively, if the positioning device first receives a userinput identifying the point of interest, for example by means of theimaging device and the display unit, the positioning device may itselfdetect when the antenna is horizontally levelled and when the phasecenter of the imaging device is placed vertically, or at least close tovertically, over the point of interest.

It will also be appreciated that the GNSS data, are continuouslycollected at the antenna of the GNSS receiving unit and the position ofthe point of interest is computed from previously collected GNSS data atthe exact time when the device is horizontally levelled and the phasecenter is vertically, or at least close to vertically, aligned with thepoint of interest. In other words, the positioning device may beconfigured to trigger the computation of the position of the GNSSantenna phase center based on the previously collected raw data uponreception of an indication that the antenna is horizontally levelled andthe phase center is vertically aligned. In other embodiments, thecollection of the raw data may occur once the indication is received.

The embodiments described in the following apply equally to the portablepositioning devices or the methods defined in the aspects andembodiments described above, unless explicitly mentioned otherwise.

The method and the portable positioning device according to the presentembodiments rely on the use of an imaging device, such as a camera, toassist in horizontally levelling the antenna together with a levellingdetector and to assist in aligning the phase center of the antennavertically over the point of interest. Accordingly, the method and theportable positioning device do not necessitate a pole with a pointingtip, which usually is heavy and cumbersome. As such, the method and theportable positioning device according to the present embodiments providefor a contactless procedure. Further, the portable positioning device islighter and more compact. The portable positioning device may behandheld like a smartphone or the like.

The embodiments of the present disclosure provide new methods andpositioning devices in which the horizontal levelling of the device canbe obtained using the levelling detector and an image captured by theimaging device, which may conveniently be displayed on the display unit.In particular, an operator of the portable positioning device may orientthe device towards the point of interest and use the display unit toidentify the point of interest within the field of view of the imagingdevice. As will be further explained in the following, indicators may,in some embodiments, be provided to indicate to the operator that theantenna is horizontally levelled. Further, the operator may also use thedisplay unit to identify whether the phase center of the GNSS antennaand the point of interest are vertically, or at least close tovertically, aligned.

In some other embodiments, the portable positioning device may beimplemented based on an existing device already including a processingunit and a display unit, to which a module including the GNSS antenna,the levelling detector (or inclinometer) and the imaging device isadded. In other embodiments based on an existing device including alsoan imaging device, the add-on module may only include a GNSS antenna anda levelling detector (inclinometer).

It will be appreciated that a position computed or obtained based on thesatellite information signals, as such, is a position at the so-called“phase center” of the GNSS antenna, which is a location generally nearthe mechanical center of the antenna. For this reason, the geospatialposition of the point of interest (or the antenna) is computed orobtained once the phase center of the antenna is vertically, or at leastclose to vertically, aligned with the point of interest.

Further, the GNSS antenna may be a single frequency antenna configuredto operate at a single frequency (L) or a multiple frequency antennaconfigured to operate at multiple frequencies (L1, L2, . . . , Ln). Inthe case of a multiple frequency antenna, the position of the phasecenter in the antenna may vary from one frequency to another. However,the phase center may be selected to correspond to the phase center forthe frequency L1.

In the absence of information about the distance from the phase centerof the antenna to the point of interest, the portable positioning deviceof the present embodiments provides a two-dimensional geospatialposition of the point of interest.

The accuracy of the two-dimensional geospatial position may depend ondifferent factors among which the accuracy of the GNSS board (or GNSSreceiver). However, using a GNSS board with a centimeter-levelprecision, a two-dimensional geospatial position with a centimeteraccuracy can be obtained since the portable positioning device or themethod enables for an accurate positioning, both horizontally andvertically, over the point of interest.

Other factors affecting the accuracy of the two-dimensional geospatialposition obtained or computed by the positioning device include forexample the accuracy of the levelling detector and the mechanicaltolerances in the arrangement of the different elements of the device. Acalibration procedure may be performed to calibrate the positioningdevice and thereby compensate for, or at least reduce, the effect ofthese variations/errors. Each positioning device may have its owncalibration model. It may be envisaged that the calibration procedure isperformed at the factory stage or on field, depending on time of useand/or changes in environmental conditions such as temperature.

As mentioned above, according to a first aspect of the presentdisclosure, it is beneficial to arrange the phase center of the GNSSantenna along, or at least close to, the sighting axis of the imagingdevice.

In some embodiments of the first aspect, the phase center of the GNSSantenna is arranged along, or at least close to, the optical axis of theimaging device. In this configuration, the sighting axis and the opticalaxis of the imaging device may therefore coincide.

According to a second aspect and other embodiments, the antenna axis isarranged to interest the sighting axis. In other words, an angle isformed between the sighting axis and the antenna axis. In the presentembodiments, a position of the fiducial marker within the field of viewof the imaging device is dependent on a distance at which thepositioning device is held above the point of interest. This distancemay be entered by an operator of the device or may be measured by meansof a distance determining module. In the present embodiments, theimaging device is inclined with respect to the antenna such that boththe optical axis and the sighting axis intersect the antenna axis.

According to a third aspect and yet other embodiments, the antenna axisand the sighting axis coincide and the optical axis intersects theantenna axis at a certain angle. In the present embodiments, aprojection center of the imaging device, through which the optical axispasses, is located on the antenna axis. Further, a fiducial markerprovided in the field of view of the imaging device for defining thesighting axis is located on the antenna axis.

By “optical axis” it is herein meant the axis of rotational symmetry ofthe imaging device, which may correspond for example to the axis passingthrough the center of a lens of the imaging device or through the centerof an image sensor (or a focal point or projection center) of theimaging device.

As mentioned above, in some embodiments, the phase center may bearranged along, or at least close to, the optical axis of the imagingdevice.

Once the operator of the portable positioning device has horizontallylevelled the antenna and positioned its phase center vertically over thepoint of interest (by means of the display unit displaying an imagecaptured by the imaging device and an input from the levelling detector,as explained above), the two-dimensional geospatial position (latitudeand longitude) of the phase center corresponds to the two-dimensionalgeospatial position of the point of interest. The two-dimensionalgeospatial position of the point of interest can therefore be obtained,or computed, based on the satellite information signals received by theantenna at this position of the positioning device.

In some other embodiments however, as mentioned above, the phase centermay be arranged along, or at least close to, the sighting axis of theimaging device. The sighting axis may be an axis used for sightingtowards a target or point of interest.

By sighting axis is herein meant an axis passing through a fiducialmaker and a projection center of the optical system of the imagingdevice, such as, for example, the center of the lens of the imagingdevice. It will be appreciated that, while the imaging device ischaracterized by a single optical axis, the sighting axis is dependenton the position of its fiducial marker. Thus, an imaging device may haveseveral sighting axes.

In some configurations, the placement of the fiducial marker is adjustedas a function of the distance (the height) of the positioning deviceover the point of interest to perform a particular measurement since,for a given sighting axis, the intersection between the sighting axisand the (ground) surface observed by the imaging device will depend onthe height at which the positioning device is held by the operator. Thedistance from the positioning device to the (ground) surface may bemeasured, or estimated, by a distance measuring module, such as a laserrangefinder or the like, or may be input by a user of the positioningdevice.

Expressed differently, it may also be appreciated that the phase centerof the GNSS antenna may be arranged within the plane in which the GNSSantenna extends. The GNSS antenna may then have an “antenna axis” whichis perpendicular to this plane and passes through the phase center. TheGNSS antenna and the imaging device may then be arranged in thepositioning device such that the sighting axis and the antenna axiscoincide, or at least almost coincide. In particular, the angle formedbetween the sighting axis and the antenna axis may be lower than fivedegrees. In this case, the height of the positioning device over the(ground) surface may be estimated with an accuracy of about +/−10centimeters to guarantee a determination of the 2D position at acentimeter-grade accuracy. Indeed, assuming that the operator makes anerror of 10 cm in estimating the height (for example inputting 1.2 meterwhile the height should be 1.3 meter), or assuming that the height ismeasured with an error of 10 cm, the error in the 2D position of thepoint of interest is equal to 10×tangent (5°) cm, i.e. 0.87 cm, which isapproximately one centimeter.

It will be appreciated that, in the configuration in which the phasecenter is aligned along the optical axis of the imaging device (and thesighting axis thereby coincides with the antenna axis and the opticalaxis of the imaging device), it is not necessary to adjust the placementof the fiducial marker and the height does not need to be determined.

Similarly, in the configuration in which the antenna axis and thesighting coincide and in which the projection center of the imagingdevice and the fiducial marker are arranged along the antenna axis, itis also not necessary to determine the height at which the positioningdevice is held above the point of interest.

In the configuration in which the antenna axis intersects both theoptical axis and the sighting axis, i.e. in the configuration in whichthe projection center of the imaging device is not along the antennaaxis, the distance from the positioning device to the point of interestis needed in order to determine the position of the fiducial marker inthe field of view of the imaging device.

Although it is an operator who manipulates the positioning device forlevelling purposes and vertical alignment, the positioning device may beconfigured to detect when the phase center of the GNSS antenna is placedvertically above the point of interest by identification of the point ofinterest in the field of view of the imaging device and based on inputfrom the levelling detector.

According to an embodiment, the processing unit may be furtherconfigured to obtain or compute a three-dimensional geospatial positionof the point of interest based on the received satellite informationsignals and a distance (or height) from the antenna to the point ofinterest.

As mentioned above, the satellite information signals are received atthe phase center of the antenna and, thus, a three-dimensionalgeospatial position computed or obtained directly by the processing unitfrom the received satellite information signals correspond to thethree-dimensional geospatial position of the phase center of theantenna. However, the target point (or point of interest) for theoperator of the portable positioning device (the “surveyor”) is not atthe antenna but rather at the point of interest visible in the field ofview of the imaging device, such as, for example, a terrain point (i.e.a point on the ground). Therefore, the three-dimensional geospatialposition of the point of interest corresponds to the three-dimensionalgeospatial position of the phase center of the antenna but compensatedfor the distance (or height) between the phase center of the antenna andthe point of interest. In other words, the altitude of thethree-dimensional geospatial position of the phase center of the antennais corrected by the distance from the phase center of the antenna to thepoint of interest when the phase center of the GNSS antenna isvertically above the point of interest and horizontally levelled inorder to collect the GNSS data for computing, or obtaining, thethree-dimensional geospatial position of the point of interest.

It will be appreciated that the point of interest does not necessarilyneed to be a terrain point but may be elevated such as a point locatedon the roof of a building.

According to an embodiment, the portable positioning device may furthercomprise a distance determining module configured to assist in obtainingthe distance from the phase center of the antenna to the point ofinterest. Based on a known spatial relationship between the phase centerof the antenna and the distance determining module, a distance from thephase center of the antenna to the point of interest may be obtained.

In some embodiments, the distance determining module may include atleast one of an electronic distance meter (EDM), an optoelectronicdistance meter, an ultrasonic sensor, a time-of-flight sensor, or acamera. Using for example an EDM or a time-of-flight sensor, thedistance between the distance determining module and the point ofinterest can be measured based on a known speed of light and the time ittakes for a light pulse to travel between the EDM, or time-of-flightsensor, and the point of interest.

Alternatively, or in addition, the distance may be obtained by means ofan imaging device or camera. It will be appreciated that the imagingdevice of the portable positioning device may, in some embodiments, beused to obtain the distance from the antenna to the point of interestbut that the portable positioning device may be equipped with anadditional camera dedicated for this purpose.

According to an embodiment, the processing unit is further configured tocollect a series of images of a ground surface, including the point ofinterest, captured by the imaging device, collect satellite informationsignals received at the antenna for at least a subset of the capturedimages and collect a reference image captured by the imaging devicebased on the indication (for example a user input) that the antenna islevelled and the phase center is vertically, or close to vertically,aligned with the point of interest (or that the point of interest isalong the sighting axis). As an alternative to, or in addition to, thecollection of satellite information signals received at the antenna, theprocessing unit may be configured to collect input from an inertialmeasurement unit (IMU) of the positioning device for at least a subsetof the captured images.

As mentioned above, the device may be configured to cause the imagingdevice to capture a series of images of a (ground) surface including thepoint of interest. In other words, a series of images, or a video, ofthe surface around, and including the point of interest, is obtainedwith the imaging device.

The positioning device may then be configured to obtain the distance tothe point of interest by means of the processing unit of the positioningdevice or a processing unit of a server in communication with thepositioning device in accordance with the following procedure.

The processing unit may be configured to orientate, in a localcoordinate system, the series of images of the ground surface capturedby the imaging device with respect to each other. A 3D reconstruction ofthe surface (in which the point of interest is located) may then begenerated in the local coordinate system using the orientated images.The surface imaged by the imagining device may be referred to as aground surface. However, as mentioned above, the point of interest isnot necessarily located on the ground.

A scale for the 3D reconstruction may then be established based oninformation relating to the motion speed of the positioning deviceduring capture of the series of images (or the scan). For this purpose,the procedure includes the collection of the positions of the antenna ina global coordinate system (i.e. a coordinate system of the GNSS) for atleast a subset of the captured images based on the collected satelliteinformation signals received at the antenna (while capturing the imagesin question). Further, following the orientation of the images in thelocal coordinate system, the positions of the imaging device for atleast some of the images of the subset in the local coordinate systemare determined. As a result, a first list including positions of theantenna in the coordinate system used by the GNSS and a second listincluding positions of the imaging device in the local coordinate systemare obtained. Based on a known spatial position of the GNSS antennarelative to the imaging device within the positioning device (which maybe referred to as an antenna offset within the positioning device) andthe information from these two lists, a scale factor between the localcoordinate system and the global coordinate system can be determined. Asa result, a scale of the 3D reconstruction can be obtained.

As an alternative, or in addition, to the use of the satelliteinformation signals collected at the GNSS antenna for at least some ofthe images of the subset, the scale factor between the local coordinatesystem and the coordinate system used by the GNSS may be establishedbased on data obtained from an inertial measurement unit (IMU) providingacceleration and gyroscopic data. The IMU may, for example, be thedevice used as a levelling detector to determine whether the antenna ishorizontally levelled. The information about the motion speed of thepositioning device during the capture of the series of images, or thevideo, may be obtained by another inertial sensor, such as anaccelerometer or the like, mounted on the portable positioning device.

Thus, a scale factor between the local coordinate system and the globalcoordinate system can be determined based on a known spatial position ofthe IMU relative to the imaging device within the positioning device,the determined positions of the IMU in the global coordinate system andthe corresponding positions of the imaging device in the localcoordinate system for the at least some images of the subset.

As mentioned above, the portable positioning device may be configured tocause the imaging device to capture a reference image when the antennais levelled and vertically, or close to vertically, aligned with thepoint of interest.

A distance from the imaging device to one or more sampling points (orpoints of a sampling area) of the 3D reconstruction located in thevicinity of the point of interest (i.e. surrounding the point ofinterest) may then be determined. This distance may then be referred toas a sampling distance as it represents a distance not to the point ofinterest but to one or more sampling points or to a sampling area. Thedistance/height from the antenna to the point of interest may then bedetermined based on the determined sampling distance, the determinedscale, the known spatial relationship between the antenna and theimaging device and the angle between the sighting axis when capturingthe reference image and a direction to one or more sampling points or tothe sampling area. Once the sampling distance and the scale have beendetermined, the distance from the imaging device to the point ofinterest may be determined using trigonometry.

It will be appreciated that, in the present procedure, the scale of the3D reconstruction of the scene may be determined based on the dataobtained from at least two images captured at two different positions ofthe imaging device involving a certain horizontal displacement (i.e. attwo different positions being non purely vertical).

According to an embodiment, the levelling detector may be arranged in aplane having a known spatial position relative to the plane in which theantenna is arranged. Information about the known spatial position of thelevelling detector relative to the plane in which the antenna isarranged in the positioning device may be input to the processing unit,or another control unit, of the portable positioning device. Theinformation may be obtained at the manufacturing stage of the portablepositioning device or via calibration. The processing unit or thecontrol unit may then derive, from such information, a position of thelevelling detector at which the antenna is horizontally levelled. Theportable positioning device may then, during levelling operations,indicate to the operator of the positioning device whether the antennais horizontally levelled based on input from the levelling detector.

According to an embodiment, the levelling detector may be arranged in aplane parallel to, or at least substantially parallel to, the plane inwhich the antenna is arranged. In the present embodiment, the levellingdetector may intentionally be arranged parallel to the antenna suchthat, when the levelling detector is horizontally levelled, the antennais then also horizontally levelled.

The levelling detector may be an instrument adapted to measure a tilt orangle with respect to gravity (or the gravitational field of Earth). Thelevelling detector may be an inclinometer (or clinometer), which mayalso be referred to as a tilt sensor. The inclinometer or tilt sensormay for example include an accelerometer to measure the tilt angle withrespect to the Earth's ground plane. In some embodiments, the levellingdetector may include an inertial measurement unit (IMU) which is anelectronic device using a combination of accelerometers and gyroscopesto provide information about the inclination of the antenna of theportable positioning device.

According to an embodiment, the portable positioning device may befurther configured to provide indicators representative of the levellingof the antenna as detected by the levelling detector (inclinometer).Different types of indicators may be envisaged to indicate to theoperator whether the antenna is horizontally levelled. The indicatorsmay also indicate how the operator is supposed to orient the portablepositioning device such that the antenna becomes horizontallyaligned/levelled.

According to an embodiment, the indicators may be displayed on thedisplay unit. In the present embodiment, visual indicators are providedto the operator via the display unit. Examples of such indicators willbe described in the following detailed embodiments.

As mentioned above, in some embodiments according to the first aspect ofthe present disclosure, the phase center of the imaging device may bearranged along the optical axis of the imaging device. Moreparticularly, in some embodiments, the phase center of the antenna maybe aligned with a center of an image sensor of the imaging device alongthe optical axis.

The imaging device may be a digital camera including an image sensorsuch as a semiconductor charge-coupled device (CCD), a complementarymetal-oxide-semiconductor (CMOS) sensor or another active digital pixelsensor. The phase center of the antenna may then be aligned with acenter of such an image sensor along the optical axis of the imagingdevice such that, when the center of the image sensor is positionedvertically over the point of interest, then the phase center of theantenna will also be positioned vertically over the point of interest. Acomputation of the satellite information signals received at the phasecenter of the antenna will then provide a 2D position of the point ofinterest and, via compensation for the distance/height from the phasecenter to the point of interest, provide a 3D position of the point ofinterest. The accuracy of the measurement will then be limited by theaccuracy of the GNSS receiver. With present GNSS technology, adetermination of the 2D or 3D position of the point of interest at acentimeter-level precision is envisaged.

According to an embodiment, the portable positioning device may furthercomprise at least one fiducial marker in the field of view of theimaging device for assisting in sighting the point of interest. Afiducial marker in the form of, for example, a cross or a dot may beprovided for assisting the operator in sighting the point of interest.The fiducial marker defines, together with the optic system of theimaging device, a sighting axis of the imaging device.

As mentioned above, in embodiments according to the second aspect of thepresent disclosure, the antenna axis may intersect both the optical axisand the sighting axis. In this configuration, the projection center ofthe imaging device is not along the antenna axis. The distance from thepositioning device to the point of interest is then used to determinethe position of the fiducial marker in the field of view of the imagingdevice.

Further, in embodiments according to the third aspect of the presentdisclosure, the antenna axis and the sighting may coincide and aprojection center of the imaging device is located along the antennaaxis. In this configuration, the fiducial marker may be arranged alongthe antenna axis.

According to an embodiment, the portable positioning device may furthercomprise a body including a first portion for holding the positioningdevice and a second portion in which at least the antenna and theinclinometer are arranged. It will be appreciated that the portablepositioning device may be implemented with different designs andarrangements of the antenna, the levelling device, the imaging deviceand the display unit. In another example, the portable positioningdevice may include a body in which the portion intended to be used forholding the positioning device also includes the antenna and theinclinometer.

It is noted that other embodiments using all possible combinations offeatures recited in the above described embodiments may be envisaged.Thus, the present disclosure also relates to all possible combinationsof features mentioned herein. Any embodiment described herein may becombinable with other embodiments also described herein, and the presentdisclosure relates to all combinations of features.

DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments will now be described in more detail, withreference to the following appended drawings:

FIG. 1 shows a portable positioning device in accordance with anembodiment;

FIG. 2 shows a portable positioning device in accordance with anembodiment;

FIG. 3 shows a portable positioning device in accordance with anembodiment;

FIGS. 4a-4c show an embodiment of a display unit of a portablepositioning device in accordance with an embodiment;

FIG. 5 shows an embodiment of a procedure for determining the distancefrom the portable positioning device to the point of interest via animaging device of the portable positioning device;

FIG. 6 illustrates at least part of a workflow, or scenario, fordetermining the distance from the antenna of the positioning device tothe point of interest;

FIG. 7 shows an example of a two-dimensional image captured by aportable positioning device in accordance with an embodiment;

FIG. 8 shows an example of a 3D reconstruction generated by a portablepositioning device in accordance with an embodiment;

FIG. 9 illustrates how the distance/height of an imaging device to apoint of interest can be determined, in accordance with an embodiment;

FIG. 10 shows a flow chart illustrating a general overview of a methodfor determining the geospatial position of a point of interest inaccordance with some embodiments;

FIG. 11 illustrates an embodiment of a positioning device in which theimaging device is arranged in an inclined position with respect to theGNSS antenna;

FIG. 12 illustrates another embodiment of a positioning device in whichthe imaging device is arranged in an inclined position with respect tothe GNSS antenna; and

FIG. 13 illustrates yet another embodiment of a positioning device inwhich the imaging device is arranged in an inclined position withrespect to the GNSS antenna.

As illustrated in the figures, the sizes of the elements and regions maybe exaggerated for illustrative purposes and, thus, are provided toillustrate the general structures of the embodiments. Like referencenumerals refer to like elements throughout.

DETAILED DESCRIPTION

Exemplifying embodiments will now be described more fully hereinafterwith reference to the accompanying drawings, in which currentlypreferred embodiments are shown. The invention may, however, be embodiedin many different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided forthoroughness and completeness, and fully convey the scope of theinvention to the skilled person.

With reference to FIG. 1, a portable positioning device 100 according toan embodiment is described.

FIG. 1 shows a portable positioning device 100 comprising an antenna110, a levelling detector 120, an imaging device 130, a display unit 140and a processing unit 150.

The antenna 110 may have a phase center 115 and may be adapted toreceive satellite information signals from a GNSS. One satellite 160 isdepicted in FIG. 1 for illustration purposes. The antenna 110 may beadapted to receive signals from four or more space-based orbitingsources (or satellites) of a GNSS. The GNSS antenna 110 may for exampleinclude an antenna patch, a ceramic element, a low noise amplifier andfilters. The GNSS antenna 110 may be lodged within a housing of theportable positioning device 100.

The GNSS signals may for example be received from any GNSS such as GPS,GLONASS, Galileo, Compass/Beidou, QZSS, SBAS, IRNSS or the like. Theantenna 110 may also be referred to as a GNSS antenna 110. The antenna110 may be connected, or may be part of, a GNSS receiver or GNSSreceiver unit or GNSS board. The GNSS receiver may be part of theprocessing unit 150 and is therefore not shown separately in FIG. 1.

The basic operation principle of a GNSS receiver, or positioning devicebased on GNSS signals, is to calculate its position by precisely timingthe signals sent by satellites of a GNSS. Each of the messagesbroadcasted by the satellites includes a time stamp indicating the timethe message was transmitted from the satellite and the satelliteposition when the message was transmitted. A distance to each of thesatellites may then be derived based on the transit time of each messageand the speed of light. Computation of these distances may result in thelocation (two- or three-dimensional position) of the positioning device.

The levelling detector 120 may be arranged relative to the antenna 110for detecting whether the antenna 110 is horizontally levelled. Thelevelling detector 120 may be an inclinometer or an inertial measurementunit (IMU) arranged relative to the antenna 110 for detecting whetherthe antenna 110 is horizontally levelled (i.e. the plane in which theantenna 110 extends is perpendicular to gravity). In the following,reference will be made to an inclinometer as a levelling detector butreference may have been equally made to an IMU. The IMU may include oneor more accelerometers and/or one or more gyroscopes and provideacceleration and gyroscopic data about the motion of the positioningdevice 100.

In particular, the inclinometer 120 may be arranged in a known spatialrelationship with respect to the antenna 110. Based on this knownspatial relationship and an input provided by the inclinometer, theprocessing unit 150 of the portable positioning device 100 can determinewhether the antenna 110 is horizontally levelled. The determination madeby the processing unit 150 may then be output to an operator of thepositioning device via the display unit 140.

In the embodiment shown in FIG. 1, the inclinometer 120 is arranged in aplane parallel, or at least substantially parallel, to the plane inwhich the antenna 110 is arranged. As such, if the inclinometer 120 isnot horizontally levelled, then the antenna 110 is not horizontallylevelled either, and vice versa.

The antenna 110 may conveniently be arranged parallel to the outsidesurface of the housing or the body of the portable positioning devicesuch that, when an operator feels that the portable positioning deviceis horizontally levelled, the antenna 110 is also horizontally levelled.

The imaging device 130 may have a sighting axis, or optical axis, 135 asdetermined by, for example, the axis or line along which there isrotational symmetry in the imaging device. In the configuration shown inFIG. 1, the optical axis and the sighting axis of the imaging devicecoincides such that reference may be made to the optical axis, and notthe sighting axis, in the following. The optical axis 135 of the imagingdevice 130 may for example correspond to the axis passing through thecenter of lens of the imaging device or the axis passing through thecenter of the image sensor of the imaging device. As mentioned, in thepresent embodiment, the optical axis 135 of the imaging device 130corresponds to the line of sight of the imaging device 130.

As shown in FIG. 1, the phase center 115 of the antenna 110 may bearranged along the optical axis 135 of the imaging device 130. In otherwords, the antenna 110 and the imaging device 130 are coaxially aligned.In particular, an image sensor of the imaging device 130 and the antenna110 may be arranged parallel, or at least substantially parallel, toeach other.

Further, the antenna 110 is arranged at a face or side of the imagingdevice 130 opposite to the face or side at which images are captured(i.e. the face sensitive to electromagnetic radiation for imaging).Expressed differently, the imaging device 130 has a sensitive area forimaging and the antenna 110 is arranged at the face or side of theimaging device opposite to the face of side at which this sensitive areais arranged.

When an operator holds the portable positioning device 100 with theimaging device 130 facing downwards for imaging the point of interest(or the ground), the antenna 110 is then arranged above the imagingdevice 130 within the portable positioning device 100. Again, thiscorresponds to the configuration of the embodiment shown in FIG. 1. Insome other embodiments, the imaging device may be arranged such that theoptical axis does not coincide with the antenna axis.

The display unit 140 may be provided for assisting an operator of theportable positioning device 100 in identifying a point of interest 180within a field of view 132 of the imaging device 130. FIG. 1 shows afront view of the display unit 140 in which an image of the groundwithin the field of view 132 of the imaging device 130 is displayed. Thepoint of interest 180 can be identified by a triangle in the imagedisplayed in the display unit 140.

FIG. 1 represents a scenario in which the portable positioning device100 may be used by an operator (not shown) wishing to obtain the 2D or3D geospatial position of the point of interest 180 located on theground. For this purpose, the operator may hold a first part or body 105of the portable positioning device 100 over a zone including the pointof interest 180.

The display unit 140 may also be adapted to assist in identifyingwhether the antenna is horizontally levelled based on an input obtainedby the inclinometer 120 and whether the phase center 115 and the pointof interest 180 are vertically aligned, or at least close to verticallyaligned.

A procedure for horizontally levelling the antenna 110 using the displayunit 140 and for vertically aligning the phase center 115 of the antenna110 with the point of interest 180 will be described in the followingwith reference to FIG. 4.

Upon reception of an indication that the antenna 110 is horizontallylevelled and the phase center 115 of the antenna 110 is vertically, orclose to vertically, aligned with the point of interest 180, thepositioning device may be configured to obtain a two-dimensionalgeospatial position of the point of interest 180 based on satelliteinformation signals 165 received at the antenna for the position of thepositioning device at which the indication has been received. Inparticular, the latitude and longitude of the phase center 115 of theantenna 110 corresponds to the latitude and the longitude of the pointof interest 180. The geospatial position of the point of interest may becomputed locally by the processing unit of the positioning device or maybe computed at a remote processing unit of for example a server locatedwithin an internet cloud infrastructure. In the latter case, thepositioning device may be configured to transmit information based onthe collected satellite information signals 165 to the remote processingunit.

Still referring to FIG. 1, the portable positioning device 100 may alsoinclude an optional distance measuring module 170 for measuring thedistance from the portable positioning device 100 to the point ofinterest 180. The processing unit 150 may then be configured to compute,or obtain, a three-dimensional geospatial position of the point ofinterest 180 based on the received satellite information signals and thedistance from the phase center 115 of the antenna 110 to the point ofinterest 180.

As mentioned above, a computation of the satellite information signalsreceived at the antenna 110 provides a 3D position of the phase center115 of the antenna 110. While the longitude and the latitude of thephase center 115 of the antenna 110 corresponds to that of the point ofinterest 180 once the antenna 110 is horizontally levelled and its phasecenter 115 is positioned vertically over the point of interest 180, thealtitude obtained by a computation of the satellite information signalsneeds to be compensated for by the distance or height from the phasecenter 115 of the GNSS antenna 110 of the positioning device 100 to thepoint of interest 180.

For this purpose, the portable positioning device 100 shown in FIG. 1may also be equipped with an optional distance determining module 170,which may for example be an electronic distance meter, an optoelectronicdistance meter, an ultrasonic sensor or a time-of-flight sensor. It willbe appreciated that the spatial position of the distance determiningmodule 170 relative to the antenna 110 in the positioning device 100 maybe known as the distance measured by the distance determining module 170to the point of interest may not exactly correspond to the distance fromthe phase center 115 of the antenna 110 to the point of interest 180 butthe distance from a point of the distance determining module 170 to thepoint of interest.

The distance determining module 170 may for example be based on ameasurement with a laser-based measurement device. In particular, alaser pulse may be emitted from the distance determining module 170towards the point of interest and part of the laser pulse may bereflected at the point of interest and then received at the distancedetermining module 170. Knowing the speed of light and the timedifference between emission of the laser pulse and reception of thereflected signal, the distance to the point of interest may bedetermined.

Once the distance between the phase center 115 of the antenna 110 andthe point of interest 180 is determined, the altitude of the point ofinterest on Earth may be computed or obtained by the processing unit 150by correcting the altitude obtained from the received satelliteinformation signals once the antenna is horizontally levelled and placedvertically over the point of interest with the determined distance.

The distance from the phase center 115 of the antenna 110 to the pointof interest 180 may also be determined using the imaging device 130 oranother imaging device or camera 170. If the imaging device 130 is used,the distance determining module 170 may not be necessary. However, thedistance may be determined even more accurately by combining the resultobtained by a distance determining module such as an electronic distancemeter and the result obtained via the imaging device 130. A procedurefor determining the distance based on the imaging device 130 will bedescribed in the following with reference to FIG. 5.

Still referring to FIG. 1, the positioning device 100 may include afirst part 105 at which the display unit 140 and the processing unit 150are arranged. The first part 105 may for example be a smartphone or thelike. The positioning device 100 then includes a second part 190 atwhich the GNSS antenna 110, the levelling detector 120, the imagingdevice 130 and the distance determining module 170 may be arranged. Aswill be further illustrated with reference to FIG. 3, the second part190 may be in the form of a module adapted to be attached and connectedto the first part 105 of the positioning device 100.

With reference to FIG. 2, a portable positioning device 200 according toanother embodiment is described.

FIG. 2 shows a portable positioning device 200 comprising an antenna 210having a phase center 215, a levelling detector 220, an imaging device230 having an optical axis 235 and a field of view 232, a display unit240, a processing unit 250 and an optional distance determining module270.

In the embodiment shown in FIG. 2, the processing unit 250 and thedisplay unit 240 are arranged in a first portion 207 of a body 205 ofthe portable positioning device 200 while the antenna 210, the levellingdetector 220 and the imaging device 230 are arranged in a second portion209 of the body 205.

The portable positioning device 200 may be equivalent to the portablepositioning device 100 described with reference to FIG. 1 except that,in the embodiment shown in FIG. 1, the first portion forms a finiteangle with respect to the second portion. It will be appreciated that,in the embodiment shown in FIG. 1, the first portion and the secondportion may define an angle of about 20-30 degrees, which may providefor a convenient use of the portable positioning device. However, inother embodiments, as shown in FIG. 2, the first portion and the secondportion may be aligned, i.e. with a zero angle.

With reference to FIG. 3, a portable positioning device 300 according toanother embodiment is described.

FIG. 3 shows a portable positioning device 300 comprising an antenna310, a levelling detector 320, an imaging device 330, a display unit 340and a processing unit 350.

FIG. 3 illustrates an embodiment in which the antenna 310, theinclinometer 320 and the imaging device 330 are provided as an add-onmodule 390 to an already existing device 305 including a processing unit350 and a display unit 340. As for the embodiment shown in FIG. 1, thepositioning device 300 may include a first part 305 at which the displayunit 340 and the processing unit 350 are arranged. The first part 305may for example be a smartphone or the like. The positioning device 300then includes a second part, the add-on module, 390 at which the GNSSantenna 310, the levelling detector 320, the imaging device 330 and theoptional distance determining module 370 may be arranged.

In some embodiments, the levelling detector 320 may be arranged at thefirst part 305 of the positioning device 300. In other words, thelevelling detector 320 may be part of the device 305 to which the module390 is connected.

With reference to FIGS. 4a-4c , an embodiment of a display unit 400 of aportable positioning device in accordance with an embodiment isdescribed.

The display unit 400, and the procedure described in the following forlevelling the antenna of the portable positioning device and forvertically aligning the phase center of the antenna with the point ofinterest, may be used in combination with any of the embodiments ofportable positioning devices described herein, such as those describedwith reference to FIGS. 1-3. FIGS. 4a-4c show a display unit 400 inwhich an image of a ground surface including a representation 480 of thepoint of interest is displayed. Indicators 402-408 may be provided inorder to horizontally level the antenna and to vertically align thephase center of the antenna with the point of interest.

The display unit 400 shows also two one-dimensional bars 402 placedalong two sides of the image in order to control the tilt of the antennaof the positioning device in two respective directions (thereby defininga plane).

In the example shown in FIGS. 4a-4c , a side dot is provided in each oneof the two bars together with an area 404 indicating where the side dotshould be within each of the respective bars such that the antennabecomes horizontally levelled. The position of the side dot along thebar corresponds to the tilt of the antenna along one direction. It istherefore controlled based on the information provided by the levellingdetector (inclinometer) of the positioning device.

As an alternative, or in addition, the display unit (or screen) 400 mayalso represent a circle 406 in which a fiducial marker 408, such as apointing or sighting dot 408, representative of the position of thephase center of the antenna in the image should be centered in order tohorizontally level the antenna. As explained above and, as will befurther illustrated in FIG. 11, if the imaging device is inclined withrespect to the plane in which the GNSS antenna is arranged, the sightingaxis of the imaging device does not coincide with the antenna axis, andthe placement of the fiducial marker may be adjusted based on the heightof the positioning device above the point of interest.

The diameter of the circle may depend on the inclination of the antennaand the GNSS accuracy.

In FIG. 4a , the antenna is not horizontally levelled and the two dotson the bars along the two sides of the image are not located within theindicated areas 404. Similarly, the sighting dot 408 is not at thecenter of the circle 406 represented on the image.

The operator may then move the portable positioning device such that thesighting dot 408 is placed within the center of the circle 406 or suchthat the side dots are arranged within the indicated areas 404 in thetwo bars 402.

Once the antenna is horizontally levelled, the side dots, the sightingdot 408 and the circle 406 may switch from being made of a dotted line,or being red, as the case may be, to being made of a continuous line, orgreen, for example. This manner of indicating that a horizontallevelling of the antenna is reached is only one example and this may beindicated to the operator in various manners. As another example, asound may be output from the positioning device once the antenna ishorizontally levelled. As yet another example, the side dots and/or thecircle may start blinking on the display unit once the antenna ishorizontally levelled.

The operator may then position the pointing or sighting dot 408 over therepresentation 480 of the point of interest in the image. The antenna isthen horizontally levelled and the phase center of the antenna isvertically aligned over the point of interest. A 2D or 3D position ofthe point of interest may then be obtained, as described above.

FIGS. 4a-4b illustrate also the workflow to be used by an operator of aportable positioning device according to the embodiments of the presentdisclosure. The workflow includes a first step in which the antennabecomes horizontally levelled, such as shown in FIGS. 4a and 4b . Theworkflow then includes a second step in which a fiducial marker (or“collimator”) is aligned with the point of interest or target seen inthe image captured by the imaging device. It will be appreciated that afiducial marker is an object placed in the field of view of the imagingdevice which appears in the image produced by the imaging device. Thefiducial marker is herein used as a point of reference assisting theoperator in sighting the point of interest. As mentioned above, theplacement of the fiducial marker will determine the sighting axis of theimaging device. Once the antenna is horizontally levelled and the phasecenter of the antenna is placed vertically over the point of interest,the GNSS data for the point of interest can be logged into the portablepositioning device in a third step.

Still referring to FIGS. 4a-4c , in order to facilitate and improve theaccuracy of the horizontal levelling of the antenna and its positioningover the point of interest, the positioning device may be configured toprovide the possibility to zoom in, or out, on the image displayed atits display unit.

Referring to FIGS. 1-3, the processing units 150, 250 and 350 (or thedevices in which these processing units are arranged) may also bereferred to as, or may also act as, data collectors. Alternatively, adata collector or a memory may be provided so that a plurality ofcoordinates for a number of point of interest may be logged and storedin the portable positioning device.

With reference to FIGS. 1 and 5-9, a procedure for determining thedistance from the positioning device 100 to the point of interest 180using the imaging device 130 is described. It will be appreciated thatthis determination may be performed as an alternative or in addition tothe determination of the distance based on a distance determining module170. Further, another imaging device or camera 170 dedicated for such adistance measurement may be provided.

Accordingly, the portable positioning device, via its processing unit150 or another control unit, may be configured to cause the imagingdevice 130 to capture a series of images of a (ground) surface includingthe point of interest 180. In other words, a scan of the surface around,and including the point of interest 180, is performed with the imagingdevice 130. This may for example be acquired while the operator, holdingthe portable positioning device with the imaging device 130 facing theground surface, approaches the point of interest 180.

As described above, the procedure for determining the distance of thepositioning device to the point of interest once the antenna ishorizontally levelled and placed vertically, or close to vertically,above the point of interest may be performed in the processing unit ofthe positioning device or in a processing unit of a server incommunication with the positioning device. In the latter case, thepositioning device is configured to transmit data collected by theimaging device, the GNSS antenna, the levelling device and/or thedisplay unit of the positioning device to the processing unit of theserver. Thus, although, it may in the following be referred to theprocessing unit of the positioning device, the computations involved inthe procedure may equally be performed at the processing unit of aserver in communication with the positioning device.

FIG. 6 illustrates an embodiment of at least part of a workflow of amethod for determining the distance of the positioning device to thepoint of interest 180. FIG. 6 shows a scenario in which the positioningdevice 100 is placed at four different positions for capturing fourdifferent images of a scene including the point of interest denoted 180.For illustration purposes, only a part of the positioning device 100 isrepresented in FIG. 6. In particular, the positioning device isrepresented by a plane 637 which may correspond to the image chip (orimage sensor) in the imaging device 130 of the positioning device 100.

In the embodiment shown in FIG. 6, the processing unit 150 of thepositioning device 100 may cause the capture of four overlapping imagesof the scene at which the point of interest 180 is located, asrepresented by the overlapping zones 632 a and 632 c of the field ofview of the imaging sensor 637. For this purpose, an operator may moveat different places and capture a series of images, such as four in thepresent example, of the scene. The four different locations at which thefour images of the scene are captured may correspond to the positions639 a, 639 b, 639 c and 639 d of the projection center of the imagingdevice 130 (the lens being not shown in FIG. 6). It will be appreciatedthat another point of the imaging device may be taken as a reference,such as for example the center of the imaging sensor 637, for theposition of the imaging device.

The positioning device 100, or rather its processing unit 150, maydefine an arbitrary local coordinate system (X₂, Y₂, Z₂). As illustratedin FIG. 6, the arbitrary coordinate system does not need to be centeredat one of the positions 639 a, 639 b, 639 c or 639 d of the imagingdevice 130 from which the images are captured. It will be appreciatedthat the positions 639 a, 639 b, 639 c and 639 d are arbitrary selectedby the operator of the positioning device 100 when capturing the images,or a video, of the scene and the positions of the imaging device in thearbitrary coordinate system (X₂, Y₂, Z₂) for the four different imagesare thus, as such, not known at the beginning of the method performed bythe processing unit 150.

FIG. 6 shows also only one satellite 660 from which GNSS signals may besent to an GNSS antenna (not shown in FIG. 6) of the positioning device100. As mentioned above, the GNSS antenna may receive signals from fouror more satellites and the signals may be computed, either by theprocessing unit 150 of the positioning device 100 itself, or aprocessing unit of server in communication with the positioning device,to determine the position of the phase center of the antenna 110 of thepositioning device 100 in an absolute coordinate system (X₁, Y₁, Z₁)relating to the GNSS.

An example of a two-dimensional image of a path border which may becaptured by the imaging device 130 is shown in FIG. 7 for illustrationpurposes. The corner of the path border may be the point of interest 180in the present example. The procedure may be repeated a number of timessuch that a plurality, or a series, of images of the path border and itssurrounding is captured.

Referring to FIG. 5, at 510, the captured images (four in the exampleshown in FIG. 6) may then be orientated in a local coordinate system(X₂, Y₂, Z₂) with respect to each other. The local coordinate system(X₂, Y₂, Z₂) is fixed with respect to the absolute coordinate system(X₁, Y₁, Z₁) of the GNSS and may be arbitrarily defined by theprocessing unit. A three-dimensional (3D) reconstruction of the scenemay then be generated, at 520, using the orientated series of capturedimages. Different techniques may be employed for orientating the imagesof the scene captured by the imaging device in a local coordinatesystem.

For example, the captured images may be orientated by identifying commoncharacteristic features among the captured images and/or by using aso-called structure from motion (SFM) technique or any otherphotogrammetric technique enabling the orientation of the images withrespect to each other based on the content of the captured imagesthemselves. For this purpose, the images to be orientated with respectto each other may overlap.

According to another example, if the levelling detector 120 is an IMU,the captured images may be orientated based on acceleration andgyroscopic data received from an IMU 120 of the positioning device 100.In other words, in this embodiment, the images may be orientated basedon data representative of the motion of the imaging device between thecapture of different images instead of being based on the content of theimages themselves.

Further, the observations of the IMU 120 when capturing the series ofimages may be used in combination with photogrammetric techniques fororientating the images in order to improve the orientation of theimages.

The positioning device 100, or rather its processing unit 150, may thenbe adapted, at 530, to generate a 3D reconstruction of the scene basedon the orientated series of images. FIG. 8 shows an example of the scenecaptured by images such as the image shown in FIG. 6, i.e. FIG. 8 showsa 3D reconstruction of the path border with its corner 180. The 3Dreconstruction may for example be displayed at the display unit 140 ofthe positioning device 100.

Turning again to FIG. 5, at 530, positions of the antenna 110 in thecoordinate system of the GNSS for at least a subset of the capturedimages may be determined based on satellite information signals receivedat the GNSS antenna 120 while capturing the images. In the presentexample, the 3D positions of the antenna 110 in the coordinate system ofthe GNSS may be determined for at least two images captured with theimaging device 130 placed at two different positions being horizontallydisplaced. Accordingly, a first list with the 3D positions of theantenna in the coordinate system used by the GNSS for some of thecaptured images (the subset) is obtained.

Further, the processing unit 150 may, at 540, determine the positions ofthe imaging device in the local coordinate system (X₂, Y₂, Z₂) for atleast some of the captured images, in particular for at least two imagesfor which the positions of the antenna in the coordinate system (X₁, Y₁,Z₁) of the GNSS have been determined.

The positions of the imaging device 130 in the local coordinate system(X₂, Y₂, Z₂) are obtained based on the orientation of the images in thelocal coordinate system (X₂, Y₂, Z₂) and are therefore obtainedsimilarly, i.e. using photogrammetry and/or based on acceleration and/orgyroscopic data received from the IMU 170 of the positioning device 100.

As a result, a second list with the 3D positions of the imaging devicein the local coordinate system for at least some images of the subset isobtained.

The processing unit may then, at 550, determine a scale of the localcoordinate system (X₂, Y₂, Z₂) based on a known spatial position of theimaging device 130 relative to the GNSS antenna 110 within thepositioning device 100 for the captured images (the antenna offset), thedetermined 3D positions of the antenna 110 in the coordinate system ofthe GNSS and the corresponding positions of the imaging device 130 inthe local coordinate system (X₂, Y₂, Z₂) for the images of the subset.

In other words, the first list of 3D positions of the antenna in theGNSS, the second list of 3D positions of the imaging device in the localcoordinate system for at least some images of the subset, and the knownspatial position of the antenna relative to the imaging device withinthe portable positioning device when capturing each one of the imagesare used by the processing unit to establish the scale of the localcoordinate system.

The processing unit may then obtain, at 560, a reference image capturedonce the antenna 110 is horizontally levelled and positioned over thepoint of interest 180.

With reference to FIGS. 5 and 9, the final part of the procedure fordetermining the distance from the antenna 110 to the point of interest180 is described.

FIG. 9 shows part of the positioning device with its GNSS antenna beinghorizontally levelled and the phase center 115 of the antenna 110 beingarranged vertically over the point of interest 180. In thisconfiguration, the optical axis 135 of the imaging device 130 isvertical and the point of interest 180 and the phase center 115 of theantenna 110 are aligned along the optical axis 135. At 570, a samplingdistance 182 from the imaging device to one or more sampling points 181or a sampling area of the 3D reconstruction located in the vicinity ofthe point of interest 180 is determined. It will be appreciated that thesampling distance 182 may be determined with respect to the nearestneighbor of the point of interest 180 in the local coordinate system orwith respect to a surface formed by one or more sampling points of the3D reconstruction that are located in the vicinity of the point ofinterest 180.

At 580, the processing unit may determine the distance (or height) fromthe antenna to the point of interest based on the determined samplingdistance 182, the antenna offset, the determined scale of the localcoordinate system and the angle α defined between the optical axis 135and a direction 182 to the sampling point 181 or a directionrepresentative of the sampling area formed by one or more samplingpoints.

As already mentioned, in some embodiments, the series of captured imagesmay be a captured video of the scene including the point of interest.

Further, the display unit may be configured to display a two-dimensionalimage 400 of the series of images, the 3D reconstruction 500 of thescene, the 3D position of the point of interest determined by theprocessing unit and/or an indication as to whether the GNSS receivingunit is activated. As another example, or in addition, the scale of the3D representation may be established based on data obtained from aninertial measurement unit, for example used as the levelling detector120 to determine whether the antenna is horizontally levelled.

Referring to the workflow described above, the images or video used toobtain a 3D reconstruction of the scene may be obtained whileapproaching the point of interest. The processing unit may then causethe reference image to be captured once the antenna is horizontallylevelled and the phase center of the antenna is vertically aligned withthe point of interest. While it is herein described that the images usedto obtain the 3D reconstruction of the scene are captured before thereference image is captured, it will be appreciated that the images usedto obtain the 3D reconstruction may be captured after the referenceimage is captured.

A general overview of a method 900 implemented in a positioning device100 is provided with reference to FIG. 9. The positioning device maycomprise an antenna adapted to receive satellite information signalsfrom a global navigation satellite system, the antenna having a phasecenter, a levelling detector arranged relative to the antenna fordetecting whether the antenna is positioned horizontally, a display unitand an imaging device having a sighting axis, wherein the phase centerof the antenna is arranged along, or at least close to, the sightingaxis. The positioning device may be a positioning device as defined inany one of the preceding embodiments.

The method may comprise determining, at 910, whether the antenna ishorizontally levelled based on an input from the levelling detector.Further, the method may include, at 920, displaying the determination onthe display unit for assisting a user in identifying whether the antennais horizontally levelled and, at 930, displaying on the display unitimages captured by the imaging device for assisting a user inidentifying a point of interest within a field of view of the imagingdevice and in identifying whether the phase center of the antenna ispositioned vertically, or at least close to vertically, above the pointof interest. At 940, the method may include triggering computation ofthe geospatial position of the point of interest based on the satelliteinformation signals received at the antenna for the position for whichan indication that the antenna is horizontally levelled and its phasecenter is positioned vertically, or at least close to vertically, overthe point of interest is received. The computation of the point ofinterest may be triggered by a user input.

It will be appreciated that all embodiments described above with respectto the different positioning devices apply to the above describedembodiment of the method.

Referring to FIG. 11, a positioning device 1100 according to anotherembodiment is described.

The positioning device 1100 is equivalent to the positioning device 100described with reference to FIG. 1 except that the imaging device 1130is arranged differently with respect to the GNSS antenna 120. Thepositioning device 1100 includes the GNSS antenna 120, a levellingdetector 125, a display unit 140, a processor 150, a distancedetermining module 170 and the imaging device 1130.

FIG. 11 illustrates a configuration in which the imaging device isinclined with respect to the plane in which the antenna 120 extends.

The present embodiment illustrates also that the imaging device 1130 hasan optical axis 1145, which corresponds to the axis of rotationalsymmetry of the imaging device, such as the axis passing through thecenter of a lens of the imaging device or through the center of an imagesensor (or a focal point or projection center) of the imaging device.

FIG. 11 illustrates also that the imaging device may have a sightingaxis 1135, which is different from the optical axis 1145 of the imagingdevice 1130. The sighting axis 1135 is the axis passing through afiducial maker and the projection center of the optical system of theimaging device, as represented by the center of an optical lens of theimaging device or by the intersection between the optical axis 1145 andthe sighting axis 1135. It will be appreciated that, for a fixedsighting axis 1135, the position of the intersection of the sightingaxis 1135 with the ground surface depends on the height at which thepositioning device 1100 is held. FIG. 11, however, shows a situation inwhich the sighting axis 1135 intersects the point of interest 1180. Inthis configuration, the placement of the fiducial marker is thereforeadjusted as a function of the distance (the height) of the positioningdevice over the point of interest to perform a particular measurement.In other words, the height of the positioning device 1100 above theground surface is used in the procedure for positioning the phase centerabove the point of interest 1180.

The distance from the positioning device to the (ground) surface may bemeasured, or estimated, by the distance measuring module 170, or may beinput by a user of the positioning device 1100. Alternatively, theheight may be determined based on a procedure based on the use of theimaging device, such as the procedure described with reference to FIG.5.

FIG. 11 illustrates also that the GNSS antenna 120 may have an antennaaxis 1115, which is the axis perpendicular to the plane in which theantenna 120 extends and passing through the phase center 115. Althoughthe angles are exaggerated in FIG. 11 for the purpose of illustration,it may be beneficial, in some embodiments, if the angle formed betweenthe sighting axis 1135 and the antenna axis 1115 is lower than fivedegrees.

Except for the above mentioned difference, all other features of theembodiments of the positioning devices and methods described withreference to FIGS. 1-10 apply also to the present embodiment.

Further, still referring to FIG. 11, a procedure for calibration of theimaging device, or rather its associated optical system, will bedescribed.

As mentioned above, the portable positioning device may further compriseat least one fiducial marker in the field of view of the imaging devicefor assisting in sighting the point of interest. The fiducial marker maybe in the form of, for example, a cross or a dot visible on the displayunit. The fiducial marker is provided for assisting the operator insighting the point of interest. A fiducial marker defines, together withthe optic system of the imaging device, a sighting axis of the imagingdevice.

Referring to FIG. 11, it is shown a sighting axis 1135, as defined by afiducial marker (not shown) of the imaging device, and an antenna axis1115. As can be seen, when the positioning device is positioned at acertain height “h” above the ground surface, the sighting axis 1135 andthe antenna axis 1115 intersects at the point of interest 1180. However,should the positioning device be held at a higher position above thepoint of interest than what is shown in FIG. 11, the sighting axis 1135would not intersect the ground surface at the point of interest 1180 butat a location on the right of the point of interest 1180 in the imageshown in FIG. 11. Similarly, should the positioning device be held at alower position above the point of interest than what is shown in FIG.11, the sighting axis 1135 would not intersect the ground surface at thepoint of interest 1180 but at a location on the left of the point ofinterest 1180. This means that, if the positioning device is not held atthe height “h”, as shown in FIG. 11, but at another height, the sightingaxis 1135 is not appropriate for sighting the point of interest 1180.

Thus, depending on the height h at which the positioning device is heldabove the point of interest, the sighting axis, and thereby the positionof the fiducial marker associated with the imaging device 130, needs tobe adjusted. For this purpose, the positioning device may be subject toa calibration procedure in which the position of the fiducial marker asa function of the height is determined. The position of the fiducialmarker in the optical system assisting the operator in sighting thepoint of interest may be expressed by its coordinates x_(cursor) andy_(cursor).

A generic calibration may be performed in factory with a plurality ofpositioning devices, wherein rods of known lengths are placed verticallybetween the antenna and a marker placed on ground. The rod may beequipped with a pointing tip for placing the rod on the marker. Theposition (x_(cursor), y_(cursor)) of the fiducial marker for a number ofrod lengths may be determined such that the sighting axis intersects themarker on the ground. The dependence of the position of the fiducialmarker as a function of the height may for example be expressed by thefollowing linear regression model:

x _(cursor) =f _(x)(h)=a _(x) /h ² +b _(x); and

y _(cursor) =f _(y)(h)=a _(y) /h ² +b _(y)

wherein a_(x), a_(y), b_(x), and b_(y) are constants defining the linearregression. The element x_(cursor) and y_(cursor) may be expressed interms of pixels (as unit) while h may be expressed in, for example,meter (m). Accordingly, b_(x), and b_(y) are also expressed in pixelsand a_(x), a_(y) are expressed in pixel/m². Another unit of length mayof course be used.

As an example, the values of a_(x), a_(y), b_(x), and b_(y) may bedetermined during a calibration procedure in factory for a plurality ofpositioning devices from the same batch (i.e. with the same arrangementof devices within the positioning device) and a plurality of heights.

Depending on the height then entered by an operator and/or determined bythe positioning device for performing a measurement, the position of thefiducial marker, and thereby the sighting axis, can be determined usingthe calibrated values of a_(x), a_(y), b_(x), and b_(y).

It is also beneficial if a calibration procedure is performed for eachone of the positioning devices, either in factory or on measurementsite, in order to tune the values of a_(x), a_(y), b_(x), and b_(y) fora specific positioning device. In other words, the values of a_(x),a_(y), b_(x), and b_(y) may be device-specific rather than beingbatch-specific. The calibration procedure may be more or less complexdepending on the number of heights for which it is performed. Using onlyone height, the values of b_(x), and b_(y) may be adjusted for aspecific device. With a plurality of heights, the values of allparameters a_(x), a_(y), b_(x), and b_(y) may be adjusted for a specificdevice.

It will be appreciated that a calibration procedure of the imagingdevice may also be performed for a positioning device in accordance withany one of the embodiments described above with reference to FIGS. 1-10,at least to compensate for errors (for example mechanical, optical andelectronical) related to the elements of the positioning device even ifthe height is not necessary for computing a two-dimensional position ofthe point of interest. In this case, the calibration procedure isperformed to align the sighting axis with the antenna axis. This is aparticular case of the above mentioned calibration procedure in whichthe terms a_(x) and a_(y) are equal to zero.

Referring to FIG. 12, a positioning device 1200 according to anotherembodiment is described.

The positioning device 1200 is equivalent to the positioning device 100described with reference to FIG. 1 except that the imaging device 1230is arranged differently with respect to the GNSS antenna 110. Thepositioning device 1200 includes the GNSS antenna 110, a levellingdetector 120, a display unit 140, a processor 150, a distancedetermining module 170 and the imaging device 1230.

FIG. 12 illustrates a configuration in which the imaging device 1230 isinclined with respect to the plane in which the antenna 110 extends. Theantenna 110 has a phase center 115 and an antenna axis 1215 which is thevertical axis passing through the phase center 115.

The present embodiment illustrates also that the imaging device 1230 hasan optical lens 1236, an image sensor 1238 and an optical axis 1245. Theimage sensor 1238 is inclined with respect to the antenna axis 1215. Theoptical axis 1245 corresponds to the axis of rotational symmetry of theimaging device, as defined by the axis passing through the center of thelens 1236 of the imaging device. In the configuration shown in FIG. 12,the optical axis passes also through the center of the image sensor 1238of the imaging device 1230. The imaging device 1230 includes aprojection center 1232 defining the field of view of the imaging device1230.

FIG. 12 illustrates also that the imaging device 1230 has a sightingaxis 1235, which is different from the optical axis 1245 of the imagingdevice 1230. In particular, the optical axis 1245 intersects both theantenna axis 1215 of the GNSS antenna and the sighting axis 1235. Thesighting axis 1235 is the axis passing through a fiducial maker 1234 andthe projection center 1232 of the optical system of the imaging device(as defined by the optical lens 1236), as represented by theintersection between the optical axis 1245 and the sighting axis 1235.In the present embodiment, the fiducial marker 1234 is, for exemplifyingpurposes, located at an extremity of the image sensor 1238. Accordingly,the point of interest 1280 is detected at a periphery of the field ofview 1239 provided by the imaging device 1230. However, as will bedescribed with reference to FIG. 13, the image sensor may be arrangeddifferently within the imaging device 1230, and in particular may bedisplaced, such that the fiducial marker is not located at an extremityof the image sensor. As an alternative to displacing the image sensorrelative to the lens 1236, such as shown in FIG. 13, the image sensor1238 together with the lens 1236 may be rotated relative to theprojection center 1232 such that the angle formed by the optical axis1235 and the sighting axis 1235 is reduced as compared to what is shownin FIG. 12. In this latter configuration, the fiducial marker would notbe placed at an extremity of the image sensor.

FIG. 12 shows a situation in which the sighting axis 1235 intersects thepoint of interest 1280, i.e. at a position at which the phase center 115of the GNSS antenna 110 is vertically above the point of interest 1280.

In this configuration, the sighting axis 1215 and the sighting axis 1235coincide such that the fiducial marker 1234, the projection center 1232and the phase center 115 are arranged along the antenna axis 1215. Inthis configuration, the position of the fiducial marker in the field ofview of the imaging device 1230 is not dependent on the distance (theheight) of the positioning device over the point of interest to performa particular measurement. When the positioning device is held with thesighting axis passing through the point of interest, as determined bymeans of the fiducial marker, the phase center of the antenna is locatedvertically above the point of interest and a two-dimensional geospatialposition of the point of interest can be determined based on thereceived satellite information signals.

Still, the distance from the positioning device to the (ground) surfacemay be measured, or estimated, by the distance measuring module 170, ormay be input by a user of the positioning device 1200, in order toobtain a 3D geospatial position of the point of interest. Alternatively,the height may be determined based on a procedure based on the use ofthe imaging device, such as the procedure described with reference toFIG. 5.

The GNSS antenna 110, the levelling detector 120, the image sensor 1230and the distance determining module 170 may be part of a first module1290 connected to another portion or module of the positioning device1200 including the display unit 140 and the processor 150.

Except for the above mentioned differences, all other features of theembodiments of the positioning devices and methods described withreference to FIGS. 1-11 apply also to the present embodiment.

With reference to FIG. 13, another embodiment of a positioning device1300 is described in which the imaging device 1330, and in particularits image sensor 1338, is inclined with respect to the plane in whichthe GNSS antenna 110 extends. In particular, the optical axis 1345 ofthe imaging device 1330 is arranged to intersect the sighting axis 1335and the antenna axis 1315.

The positioning device 1300 shown in FIG. 13 is equivalent to thepositioning device 1200 described with reference to FIG. 12 except thatthe position of the image sensor 1338 within the imaging device 1330,and in particular relative to the projection center 1332 of the imagingdevice 1330, has been moved. More specifically, as compared to theconfiguration shown in FIG. 12, the image sensor 1338 has beentranslated along a direction parallel to the lens 1336. In the presentconfiguration, the optical axis 1345 does not pass through the center ofthe image sensor 1338. Still, the optical axis 1345 is defined as theaxis passing through the projection center 1332 and through the centerof the optical lens 1336. The optical axis 1345 is also perpendicular tothe image sensor 1338. In the present configuration, the fiducial marker1334 is arranged on the image sensor 1338 but not at an extremity of theimage sensor 1338. In the present configuration, the sighting axis 1335and the antenna axis 1315 coincide such that the fiducial marker 1334,the projection center 1332 and the phase center 115 of the GNSS antennaare located on the antenna axis 1315. FIG. 13 also shows the field ofview 1339 provided by the imaging device 1330.

Except for the above mentioned difference, all other features of theembodiments of the positioning devices and methods described withreference to FIGS. 1-12 apply also to the present embodiment.

It will be appreciated that the embodiments described with reference toFIGS. 11-13 are beneficial in that the imaging device is inclined withrespect to the antenna axis, thereby providing an improved field ofview, looking forward instead of right under the positioning device(thereby not showing the operator's feet in the field of view).

The person skilled in the art realizes that the present invention by nomeans is limited to the preferred embodiments described above. On thecontrary, many modifications and variations are possible within thescope of the appended claims.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. In the above, a processor or processingunit may include, by way of example, a general purpose processor, aspecial purpose processor, a conventional processor, a digital signalprocessor (DSP), a plurality of microprocessors, one or moremicroprocessors in association with a DSP core, and any other type ofintegrated circuit (IC).

Further, although applications of the positioning device have beendescribed with reference to surveying systems, the invention may be usedin other applications and/or systems.

Additionally, variations to the disclosed embodiments can be understoodand effected by the skilled person in practicing the claimed invention,from a study of the drawings, the disclosure, and the appended claims.In the claims, the word “comprising” does not exclude other elements,and the indefinite article “a” or “an” does not exclude a plurality. Themere fact that certain features are recited in mutually differentdependent claims does not indicate that a combination of these featurescannot be used to advantage.

1. A portable positioning device for obtaining a geospatial position ofa point of interest, said portable positioning device comprising: anantenna adapted to receive satellite information signals from a globalnavigation satellite system, GNSS, said antenna having a phase centerand an antenna axis, which is a vertical axis passing through the phasecenter; a levelling detector arranged relative to said antenna fordetecting whether said antenna is positioned horizontally; an imagingdevice having a sighting axis, which is an axis passing through afiducial marker provided in a field of view of the imaging device forassisting in sighting the point of interest, wherein the position of thefiducial marker within said field of view is dependent on a distance atwhich the positioning device is held above the point of interest andwherein the antenna axis intersects the sighting axis; a display unitfor assisting in identifying said point of interest within said field ofview of said imaging device and for assisting in identifying whethersaid antenna is horizontally levelled based on an input from saidlevelling detector and whether said point of interest is along saidsighting axis; and a processing unit for triggering computation of thegeospatial position of said point of interest based on the informationsatellite signals received at said antenna for a position of thepositioning device for which an indication that said antenna ishorizontally levelled and that said point of interest is along saidsighting axis is received.
 2. The portable positioning device of claim1, wherein the processing unit is further configured to compute ageospatial position of said point of interest based on the receivedsatellite information signals or wherein the positioning device isconfigured to transmit information based on the received satelliteinformation signals to a server, or an external device, for computationof a geospatial position of said point of interest based on saidinformation and to receive the computed geospatial position from saidserver or said external device.
 3. The portable positioning device ofclaim 1, further comprising a distance determining module configured toassist in obtaining a distance from said antenna to said point ofinterest.
 4. The portable positioning device of claim 3, wherein thedistance determining module includes at least one of an electronicdistance meter, an optoelectronic distance meter, an ultrasonic sensor,a time-of-flight sensor or a camera.
 5. The portable positioning deviceof claim 1, wherein the processing unit is further configured to:collect a series of images of a ground surface, including said point ofinterest, captured by said imaging device; collect satellite informationsignals received at the antenna for at least a subset of the capturedimages and/or collect input from an inertial measurement unit (IMU) ofthe positioning device for at least a subset of the captured images; andcollect a reference image captured by said imaging device based on saidindication that said antenna is levelled and that said point of interestis along said sighting axis.
 6. The portable positioning device of claim5, further configured to obtain a distance from said antenna to saidpoint of interest by means of said processing unit of the positioningdevice or a processing unit of a server, or an external device, incommunication with said positioning device, said processing unit beingconfigured to: orientate, in a local coordinate system (X₂, Y₂, Z₂), thecollected series of images of the ground surface with respect to eachother; generate a three-dimensional (3D) reconstruction of the groundsurface using the orientated images in said local coordinate system;determine positions of the antenna in a global coordinate system (X₁,Y₁, Z₁) for said at least a subset of the captured images based on thecollected satellite information signals received at the antenna for saidat least a subset of the captured images; determine positions of theimaging device for at least some images of said subset in said localcoordinate system based on the orientated images; determine a scalefactor between the local coordinate system and the global coordinatesystem based on a known spatial position of the antenna relative to saidimaging device within said positioning device, the determined positionsof the antenna in the global coordinate system and the correspondingpositions of the imaging device in the local coordinate system for saidat least some images of said subset; determine, in the local coordinatesystem, a sampling distance from said imaging device to one or moresampling points, or a sampling area, of the 3D reconstruction located inthe vicinity of said point of interest; and determine the distance fromsaid antenna to said point of interest based on the sampling distance,the determined scale, the known spatial position of the antenna relativeto said imaging device within said positioning device and the angledefined between the sighting axis while capturing the reference imageand a direction to said one or more sampling points, or a directionrepresentative of said sampling area.
 7. The portable positioning deviceof claim 5, further configured to obtain a distance from said antenna tosaid point of interest by means of said processing unit of thepositioning device or a processing unit of a server, or an externaldevice, in communication with said positioning device, said processingunit being configured to: orientate, in a local coordinate system (X₂,Y₂, Z₂), the collected series of images of the ground surface withrespect to each other; generate a three-dimensional (3D) reconstructionof the ground surface using the orientated images in said localcoordinate system; obtain positions of the IMU in a global coordinatesystem (X₁, Y₁, Z₁) for said at least a subset of the captured imagesbased on the collected input from the IMU; determine positions of theimaging device for at least some images of said subset in said localcoordinate system based on the orientated images; determine a scalefactor between the local coordinate system and the global coordinatesystem based on a known spatial position of the IMU relative to saidimaging device within said positioning device, the determined positionsof the IMU in the global coordinate system and the correspondingpositions of the imaging device in the local coordinate system for saidat least some images of said subset; determine, in the local coordinatesystem, a sampling distance from said imaging device to one or moresampling points, or a sampling area, of the 3D reconstruction located inthe vicinity of said point of interest; and determine the distance fromsaid antenna to said point of interest based on the sampling distance,the determined scale, the known spatial position of the IMU relative tosaid imaging device within said positioning device and the angle definedbetween the sighting axis while capturing the reference image and adirection to said one or more sampling points, or a directionrepresentative of said sampling area.
 8. The portable positioning deviceof claim 1, wherein the levelling detector is arranged in a plane havinga known position relative to the plane in which the antenna is arrangedor in a plane parallel to, or at least substantially parallel to, theplane in which said antenna is arranged.
 9. The portable positioningdevice of claim 1, wherein the levelling detector is one of aninclinometer and/or an inertial measurement unit.
 10. The portablepositioning device of claim 1, being further configured to provideindicators representative of the levelling of said antenna as detectedby said levelling detector.
 11. The portable positioning device of claim10, wherein said indicators are displayed on said display unit.
 12. Theportable positioning device of claim 1, further comprising a bodyincluding a first portion for holding said positioning device and asecond portion in which at least said antenna and said levellingdetector are arranged.
 13. A portable positioning device for obtaining ageospatial position of a point of interest, said portable positioningdevice comprising: an antenna adapted to receive satellite informationsignals from a global navigation satellite system, GNSS, said antennahaving a phase center and an antenna axis being an axis passing throughsaid phase center and perpendicular to a plane in which said antennaextends; a levelling detector arranged relative to said antenna fordetecting whether said antenna is positioned horizontally; an imagingdevice having an optical axis, wherein the imaging device is inclinedwith respect to the antenna such that the optical axis intersects theantenna axis and wherein a projection center of the imaging device,through which the optical axis passes, is located on the antenna axis; adisplay unit for assisting in sighting said point of interest using asighting axis and for assisting in identifying whether said antenna ishorizontally levelled based on an input from said levelling detector,wherein said sighting axis passes through said projection center and afiducial marker provided in a field of view of the imaging device forassisting in sighting the point of interest, said fiducial marker beinglocated on the antenna axis; and a processing unit for triggeringcomputation of the geospatial position of said point of interest basedon the information satellite signals received at said antenna for aposition of the positioning device for which an indication that saidantenna is horizontally levelled and that said point of interest isalong said sighting axis is received.
 14. The portable positioningdevice of claim 13, wherein the processing unit is further configured tocompute a geospatial position of said point of interest based on thereceived satellite information signals or wherein the positioning deviceis configured to transmit information based on the received satelliteinformation signals to a server, or an external device, for computationof a geospatial position of said point of interest based on saidinformation and to receive the computed geospatial position from saidserver or said external device.
 15. The portable positioning device ofclaim 13, further comprising a distance determining module configured toassist in obtaining a distance from said antenna to said point ofinterest.
 16. The portable positioning device of claim 13, wherein theprocessing unit is further configured to: collect a series of images ofa ground surface, including said point of interest, captured by saidimaging device; collect satellite information signals received at theantenna for at least a subset of the captured images and/or collectinput from an inertial measurement unit (IMU) of the positioning devicefor at least a subset of the captured images; and collect a referenceimage captured by said imaging device based on said indication that saidantenna is levelled and that said point of interest is along saidsighting axis.
 17. The portable positioning device of claim 16, furtherconfigured to obtain a distance from said antenna to said point ofinterest by means of said processing unit of the positioning device or aprocessing unit of a server, or an external device, in communicationwith said positioning device, said processing unit being configured to:orientate, in a local coordinate system (X₂, Y₂, Z₂), the collectedseries of images of the ground surface with respect to each other;generate a three-dimensional (3D) reconstruction of the ground surfaceusing the orientated images in said local coordinate system; determinepositions of the antenna in a global coordinate system (X₁, Y₁, Z₁) forsaid at least a subset of the captured images based on the collectedsatellite information signals received at the antenna for said at leasta subset of the captured images; determine positions of the imagingdevice for at least some images of said subset in said local coordinatesystem based on the orientated images; determine a scale factor betweenthe local coordinate system and the global coordinate system based on aknown spatial position of the antenna relative to said imaging devicewithin said positioning device, the determined positions of the antennain the global coordinate system and the corresponding positions of theimaging device in the local coordinate system for said at least someimages of said subset; determine, in the local coordinate system, asampling distance from said imaging device to one or more samplingpoints, or a sampling area, of the 3D reconstruction located in thevicinity of said point of interest; and determine the distance from saidantenna to said point of interest based on the sampling distance, thedetermined scale, the known spatial position of the antenna relative tosaid imaging device within said positioning device and the angle definedbetween the sighting axis while capturing the reference image and adirection to said one or more sampling points, or a directionrepresentative of said sampling area.
 18. The portable positioningdevice of claim 16, further configured to obtain a distance from saidantenna to said point of interest by means of said processing unit ofthe positioning device or a processing unit of a server, or an externaldevice, in communication with said positioning device, said processingunit being configured to: orientate, in a local coordinate system (X₂,Y₂, Z₂), the collected series of images of the ground surface withrespect to each other; generate a three-dimensional (3D) reconstructionof the ground surface using the orientated images in said localcoordinate system; obtain positions of the IMU in a global coordinatesystem (X₁, Y₁, Z₁) for said at least a subset of the captured imagesbased on the collected input from the IMU; determine positions of theimaging device for at least some images of said subset in said localcoordinate system based on the orientated images; determine a scalefactor between the local coordinate system and the global coordinatesystem based on a known spatial position of the IMU relative to saidimaging device within said positioning device, the determined positionsof the IMU in the global coordinate system and the correspondingpositions of the imaging device in the local coordinate system for saidat least some images of said subset; determine, in the local coordinatesystem, a sampling distance from said imaging device to one or moresampling points, or a sampling area, of the 3D reconstruction located inthe vicinity of said point of interest; and determine the distance fromsaid antenna to said point of interest based on the sampling distance,the determined scale, the known spatial position of the IMU relative tosaid imaging device within said positioning device and the angle definedbetween the sighting axis while capturing the reference image and adirection to said one or more sampling points, or a directionrepresentative of said sampling area.
 19. The portable positioningdevice of claim 13, wherein the levelling detector is arranged in aplane having a known position relative to the plane in which the antennais arranged or in a plane parallel to, or at least substantiallyparallel to, the plane in which said antenna is arranged.
 20. Theportable positioning device of claim 13, wherein the levelling detectoris one of an inclinometer and/or an inertial measurement unit.